/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.web.reactive.result.view;

import java.util.function.Supplier;

import org.reactivestreams.Publisher;
import org.reactivestreams.Subscription;
import reactor.core.publisher.BaseSubscriber;
import reactor.core.publisher.Mono;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.LeakAwareDataBufferFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseCookie;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.util.MultiValueMap;

/**
 * Response that subscribes to the writes source but never posts demand and also
 * offers method to then cancel the subscription, and check of leaks in the end.
 *
 * @author Rossen Stoyanchev
 */
public class ZeroDemandResponse implements ServerHttpResponse {

    private final LeakAwareDataBufferFactory bufferFactory;

    private final ZeroDemandSubscriber writeSubscriber = new ZeroDemandSubscriber();


    public ZeroDemandResponse() {
        this.bufferFactory = new LeakAwareDataBufferFactory();
    }


    public void checkForLeaks() {
        this.bufferFactory.checkForLeaks();
    }

    public void cancelWrite() {
        this.writeSubscriber.cancel();
    }


    @Override
    public DataBufferFactory bufferFactory() {
        return this.bufferFactory;
    }

    @Override
    public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
        body.subscribe(this.writeSubscriber);
        return Mono.never();
    }


    @Override
    public boolean setStatusCode(HttpStatus status) {
        throw new UnsupportedOperationException();
    }

    @Override
    public HttpStatus getStatusCode() {
        throw new UnsupportedOperationException();
    }

    @Override
    public MultiValueMap<String, ResponseCookie> getCookies() {
        throw new UnsupportedOperationException();
    }

    @Override
    public void addCookie(ResponseCookie cookie) {
        throw new UnsupportedOperationException();
    }

    @Override
    public void beforeCommit(Supplier<? extends Mono<Void>> action) {
        throw new UnsupportedOperationException();
    }

    @Override
    public boolean isCommitted() {
        throw new UnsupportedOperationException();
    }

    @Override
    public Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
        throw new UnsupportedOperationException();
    }

    @Override
    public Mono<Void> setComplete() {
        throw new UnsupportedOperationException();
    }

    @Override
    public HttpHeaders getHeaders() {
        throw new UnsupportedOperationException();
    }


    private static class ZeroDemandSubscriber extends BaseSubscriber<DataBuffer> {

        @Override
        protected void hookOnSubscribe(Subscription subscription) {
            // Just subscribe without requesting
        }
    }
}
